There are lots of Europeans and Chinese people and Indians at Microsoft, I'm sure. But you'd be surprised at how hard it is to get even qualified workers into the US. Many of my friends just graduated from a very good US university and were able to land extremely lucrative jobs in Wall Street, but had to forgo those offers because of the government's refusal to give them even an H1B visa. Take a look at the news of Microsoft's new office in Vancouver. That's about 2 hours from Seattle by car, so the only reason it exists is to deal with the visa problem.

And even though Eastern Europe and India are huge talent pools, the cream of those crops is still not huge. I'm the son of an Indian immigrant, but I'll be the first to tell you that the majority of Indian IT people I've run into are not that impressive, just like with IT people from anywhere else. It takes a lot of effort to get the right people and reject the wrong ones... especially when from overseas because mistakes there are especially costly.